Initially, I just wired in a manual switch and noted about a 15 degree drop in temp. Prior to the manual switch the gauge ran between the "R" or"M" in 100 degree ambient temps with no A/C and the Steeda radiator. After adding the manual fan switch, the gauge ran on the "O" in similar ambient conditions.
Two things I didn't like about the manual fan switch were that the fan would run continually unless the switch was manually turned off and that it would start running as soon as the ignition was turned on. My concern was that the life of the fan may be adversely affected by such constant operation and that the heavy current draw of the fan ( somewhere around 20 amps) would put a strain on the electrical system upon start-up. I'm not sure if the fan is one of the electrical devices deactivated during start-up.
In any case, the combination of a manual fan switch in combination with an auxilliary fan controllor with a lower temperature range that the factory settings just seemed like a good idea. Plus, the ability to switch to the factory EEC-V fan controllor is permitted.
I selected a Hayden non-adjustable fan switch kit (P/N 3652). It was $26 at Pep Boys. A Hayden adjustable fan controller (90 degrees F to 210 degrees F) is also available for about $35. The Hayden non-adjustable kit includes a snap switch, an activation relay and a wiring harness. The snap switch snaps from an open position to a closed position at 185 F and back to an open position at 165 degrees F. For the wiring arrangement described herein, a three-position switch is also needed. With the non-adjustable controller and the three-position switch, the total cost of this mod was under $30.
The Hayden instructions describe wiring the activation relay to provide power directly to the fan. The mod discussed herein wires the activation relay to close a ground circuit to the EEC-V processor high-speed fan controller circuit when the snap switch moves to the closed position. The wireing arrangement described herein permits the three different fan operating conditions mentioned above.
The diagram and pictures below provide details of the installation. IMPORTANT: Tap into the high-speed fan controller wire (pin 46 on 4.6L Cobra). Do not break the original continuity of this wire.
I used a little two-part putty to secure the snap switch in place on the radiator. The putty provides a solid mounting arrangement. The kit does include a mounting clip for the snap switch. But, having previously used one of these kits on another Mustang, I found that the provided clip allows the snap switch and probe to work loose, causing problems with accurately monitoring temperature of the radiator.
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